In response to the demands of consumers who are driven both by ever-escalating fuel prices and the dire consequences of global warming, the automobile industry is slowly starting to embrace the need for ultra-low emission, high efficiency cars. While some within the industry are attempting to achieve these goals by engineering more efficient internal combustion engines, others are incorporating hybrid or all-electric drive trains into their vehicle line-ups. To meet consumer expectations, however, the automobile industry must not only achieve a greener drive train, but must do so while maintaining reasonable levels of performance, range, reliability, safety and cost.
The most common approach to achieving a low emission, high efficiency car is through the use of a hybrid drive train in which an internal combustion engine (ICE) is combined with one or more electric motors. While hybrid vehicles provide improved gas mileage and lower vehicle emissions than a conventional ICE-based vehicle, due to their inclusion of an internal combustion engine they still emit harmful pollution, albeit at a reduced level compared to a conventional vehicle. Additionally, due to the inclusion of both an internal combustion engine and an electric motor(s) with its accompanying battery pack, the drive train of a hybrid vehicle is typically more complex than that of either a conventional ICE-based vehicle or an all-electric vehicle, resulting in increased cost and weight. Accordingly, several vehicle manufacturers are designing vehicles that only utilize an electric motor, thereby eliminating one source of pollution while significantly reducing drive train complexity.
While vehicle manufacturers may achieve the benefits of an all-electric vehicle using a single electric motor, the efficiency and traction control offered my multi-motor configurations has led to the development of alternative drive train control systems. For example, U.S. Patent Publication No. 2010/0194318 discloses an electric vehicle that includes multiple drive motors, multiple power supplies, multiple inverters and a single DC-DC power converter. A control circuit coupled to both the power supplies and the inverters provides instructions to each, thus allowing the system to efficiently utilize the multiple motors while taking advantage of the output characteristics of each power supply. In an alternate configuration disclosed in U.S. Pat. No. 8,761,985, a pair of motors with a shared transmission provides a means of optimizing the torque applied by each of the motors. A method of optimizing the torque is described that takes into account wheel slip.
While a variety of hybrid and all-electric vehicles are known, an improved multi-motor configuration is needed with improved power output and efficiency. The present invention provides such an improved drive system.